Gary,
I can see why people might not want to use an airstone in fish that have been shipped overnight - the carbon dioxide builds up and lowers the pH (even though the dissolved oxygen may still be nice and high). If you aerate that water, it drives the CO2 off, but then the ammonia in the bag becomes deadly toxic at a high pH. I've seen fish literally die in the acclimation bag when that is done.
However, you local store knows that ammonia isn't going to be a problem in the short time it takes you to get home. Additionally, most stores don't use oxygen to fill the bags, just air. If you just float fish like that without an airstone, and do it too long, the fish can become hypoxic.
So the difference in what you are hearing is due to different conditions inside the shipping bag.
Jay
